Power apparatus, current detecting circuit and current detecting method

ABSTRACT

A power apparatus, a current detecting circuit and a current detecting method are provided. The power apparatus includes a power conversion circuit and the current detecting circuit. The power conversion circuit generates an output current. The current detecting circuit includes first and second current sensing resistors and a control circuit. The first current sensing resistor and the second current sensing resistor sense the output current to generate first and second sensing voltage, respectively. The control circuit receives the first sensing voltage and the second sensing voltage, and converts the first sensing voltage and the second sensing voltage respectively into a first current sensing value and a second current sensing value. The control circuit triggers a protection mechanism when the first current sensing value is greater than a first overcurrent protection value. In the case where the first current sensing value is not greater than the first overcurrent protection value, the control circuit triggers the protection mechanism if the second current sensing value is greater than a second overcurrent protection value. The first overcurrent protection value is greater than the second overcurrent protection value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan Application No.107133913, filed on Sep. 26, 2018. The entirety of the above-mentionedpatent application is hereby incorporated by reference herein and made apart of this specification.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a power apparatus, and more particularly, to apower apparatus and a current sensing circuit thereof in compliance withlimited power source (LPS) and a current detecting method.

2. Description of Related Art

With the advancement of technology, electronic information products havebecome an indispensable tool in people's daily lives. Various powerapparatus have emerged to provide the power required for the operationof electronic information products. Further, in order to ensure thesafety of the power apparatus, the power apparatus needs to pass varioussafety tests.

Specifically, as specified in the safety standard IEC 60950-1, theelectronic information products are required to have a suitablefireproof enclosure. Yet, it is also specified that, when the power ofthe electronic information products is provided by the limited powersource (LPS), if electronic components therein are mounted on a printedcircuit board with the fire-proof level of V-1 or higher, the electronicinformation products do not need to have the fireproof enclosure.Therefore, suppliers of the electronic information products usuallydemand that the power apparatus can be comply with the requirements ofthe limited power source.

However, for allowing the power apparatus to pass test items of thepower limited source, it is usually necessary to additionally dispose adetecting circuit in the power apparatus. To prevent the detectingcircuit from affecting a conversion efficiency of the power apparatus,the detecting circuit is usually disposed with a detecting resistor witha very small resistance. In addition, in order to obtain accuratedetecting values, the detecting resistor needs to be additionallydisposed with an amplifying circuit, which will increase themanufacturing cost of the power apparatus. Therefore, how to allow thepower apparatus to pass the test items of the power limited source whileavoiding adding too much manufacturing cost is one of the major issuesfaced by those skilled in the art.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a power apparatus, a currentdetecting circuit and a current detecting method to not only allow thepower apparatus to pass the test items of the limited power source, butalso to prevent a significant increase in the manufacturing cost of thepower apparatus.

The current detecting circuit of the invention includes a first currentsensing resistor, a second current sensing resistor and a controlcircuit. The first current sensing resistor is configured to sense anoutput current of a power apparatus to generate a first sensing voltage.The second current sensing resistor is configured to sense the outputcurrent to generate a second sensing voltage. The control circuit iscoupled to two ends of the first current sensing resistor and two endsof the second current sensing resistor to receive the first sensingvoltage and the second sensing voltage, and converts the first sensingvoltage and the second sensing voltage respectively into a first currentsensing value and a second current sensing value. The control circuittriggers a protection mechanism when the first current sensing value isgreater than a first overcurrent protection value. In the case where thefirst current sensing value is not greater than the first overcurrentprotection value, the control circuit triggers the protection mechanismif the second current sensing value is greater than a second overcurrentprotection value. Here, the first overcurrent protection value isgreater than the second overcurrent protection value.

In an embodiment of the invention, when the first current sensing valueis not greater than the first overcurrent protection value, if the firstcurrent sensing value is equal to a reference current value and thesecond current sensing value is greater than the second overcurrentprotection value, the control circuit determines that the first currentsensing resistor is shorted, and the control circuit triggers theprotection mechanism to limit the output current. Here, the referencecurrent value is less than the second overcurrent protection value.

In an embodiment of the invention, the reference current value is a zerocurrent value.

In an embodiment of the invention, the control circuit includes anamplifying circuit, a first analog-to-digital conversion circuit, asecond analog-to-digital conversion circuit and a control body. Theamplifying circuit is coupled to the two ends of the first currentsensing resistor to amplify the first sensing voltage and accordinglygenerate an amplified voltage. The first analog-to-digital conversioncircuit is coupled to the amplifying circuit to receive the amplifiedvoltage and perform an analog-to-digital conversion on the amplifiedvoltage to generate the first current sensing value. The secondanalog-to-digital conversion circuit is directly coupled to the two endsof the second current sensing resistor, and configured to perform theanalog-to-digital conversion on the second sensing voltage andaccordingly generate the second current sensing value. The control bodyis coupled to the first analog-to-digital conversion circuit and thesecond analog-to-digital conversion circuit to receive the first currentsensing value and the second current sensing value. When the firstcurrent sensing value is not greater than the first overcurrentprotection value, if the first current sensing value is equal to areference current value and the second current sensing value is greaterthan the second overcurrent protection value, the control bodydetermines that the first current sensing resistor is shorted, and thecontrol body triggers the protection mechanism to limit the outputcurrent. Here, the reference current value is less than the secondovercurrent protection value.

The power apparatus of the invention includes a power conversion circuitand the current detecting circuit. The power conversion circuit isconfigured to generate an output current. The current detecting circuitis coupled to the power conversion circuit to detect the output current.The current detecting circuit includes a first current sensing resistor,a second current sensing resistor and a control circuit. The firstcurrent sensing resistor is configured to sense the output current togenerate a first sensing voltage. The second current sensing resistor isconfigured to sense the output current to generate a second sensingvoltage. The control circuit is coupled to two ends of the first currentsensing resistor and two ends of the second current sensing resistor toreceive the first sensing voltage and the second sensing voltage, andconverts the first sensing voltage and the second sensing voltagerespectively into a first current sensing value and a second currentsensing value. The control circuit triggers a protection mechanism whenthe first current sensing value is greater than a first overcurrentprotection value. In the case where the first current sensing value isnot greater than the first overcurrent protection value, the controlcircuit triggers the protection mechanism if the second current sensingvalue is greater than a second overcurrent protection value. Here, thefirst overcurrent protection value is greater than the secondovercurrent protection value.

The current detecting method of the invention includes following steps.An output current of a power apparatus is sensed by a first currentsensing resistor to obtain a first sensing voltage. The output currentis sensed by a second current sensing resistor to obtain a secondsensing voltage. The first sensing voltage and the second sensingvoltage are respectively converted into a first current sensing valueand a second current sensing value by a control circuit. A protectionmechanism is triggered by the control circuit if the first currentsensing value is greater than a first overcurrent protection value. Inthe case where the first current sensing value is not greater than thefirst overcurrent protection value, the protection mechanism istriggered by the control circuit if the second current sensing value isgreater than a second overcurrent protection value. Here, the firstovercurrent protection value is greater than the second overcurrentprotection value.

Based on the above, the power apparatus, the current detecting circuitand the current detecting method provided by the embodiments of theinvention can allow the control circuit to correctly trigger theprotection mechanism by a determination condition “the first currentsensing value is not greater than the first overcurrent protection valueand the second current sensing value is greater than the secondovercurrent protection value”. In this way, not only can the powerapparatus successfully pass the test items of the limited power source,the manufacturing cost of the power apparatus may also be reduced.

To make the above features and advantages of the disclosure morecomprehensible, several embodiments accompanied with drawings aredescribed in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments of thedisclosure and, together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a circuit block diagram illustrating a power apparatusaccording to an embodiment of the invention.

FIG. 2 is a circuit block diagram illustrating a control circuitaccording to an embodiment of the invention.

FIG. 3 is a flowchart illustrating steps in the current detecting methodaccording to an embodiment of the invention.

FIG. 4 is a flowchart illustrating detailed steps in step S330 of FIG. 3according to an embodiment of the invention.

FIG. 5 is a flowchart illustrating detailed steps in step S340 of FIG. 3according to an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

In order to make content of the invention more comprehensible,embodiments are described below as the examples to prove that theinvention can actually be realized. In addition, whenever possible,identical or similar reference numbers stand for identical or similarelements in the figures and the embodiments.

FIG. 1 is a circuit block diagram illustrating a power apparatusaccording to an embodiment of the invention. With reference to FIG. 1, apower apparatus 100 includes a power conversion circuit 120 and acurrent detecting circuit 140. The power conversion circuit 120 isconfigured to generate an output voltage Vo and an output current Io forproviding the power required by a load to operate. The current detectingcircuit 140 is coupled to the power conversion circuit 120 to detect theoutput current Io.

To be specific, the current detecting circuit 140 includes a firstcurrent sensing resistor R1, a second current sensing resistor R2 and acontrol circuit 143. The first current sensing resistor R1 is configuredto sense the output current Io to generate a first sensing voltage VS1.The second current sensing resistor R2 is configured to sense the outputcurrent Io to generate a second sensing voltage VS2. The control circuit143 is coupled to two ends of the first current sensing resistor R1 andtwo ends of the second current sensing resistor R2 to receive the firstsensing voltage VS1 and the second sensing voltage VS2. The controlcircuit 143 converts the first sensing voltage VS1 and the secondsensing voltage VS2 respectively into a first current sensing value CS1and a second current sensing value CS2. The control circuit 143 candetermine whether to trigger a protection mechanism according to thefirst current sensing value CS1 and the second current sensing valueCS2.

More specifically, in the case where the first current sensing resistorR1 and the second current sensing resistor R2 are both normal, when theoutput current Io is less than an overcurrent value, the first currentsensing value CS1 will be less than a first overcurrent protection valueOCP1 and the second current sensing value CS2 will also be less than asecond overcurrent protection value OCP2. Accordingly, the controlcircuit 143 can determine that the power apparatus 100 is operatingnormally without triggering the protection mechanism. Conversely, whenthe output current Io is greater than the overcurrent value, the firstcurrent sensing value Cl will be greater than the first overcurrentprotection value OCP1, and thus the control circuit 143 can determinethat the power apparatus 100 is operating abnormally and trigger theprotection mechanism.

In addition, when the power apparatus 100 is subject to the limitedpower source (LPS) test, the first current sensing resistor R1 will beshorted to simulate whether the power apparatus 100 can pass the limitedpower source test in the event of a single component failure. Since thefirst current sensing resistor R1 is shorted, even if the output currentIo is greater than the overcurrent value, the first sensing voltage VS1received by the control circuit 143 is still extremely small so thefirst current sensing value CS1 would not be greater than the firstover-current protection value OCP1. In this case, the control circuit143 can then determine whether to trigger the protection mechanismaccording to the second current sensing value CS2 so the power apparatus100 can pass the limited power source test. In detail, in the case wherethe first current sensing value CS1 is not greater than the firstovercurrent protection value OCP1, if the second current sensing valueCS2 is greater than the second overcurrent protection value OCP2, thecontrol circuit 143 can determine that the output current Io is greaterthan the overcurrent value and accordingly trigger the protectionmechanism. Here, the first overcurrent protection value OCP1 is greaterthan the second overcurrent protection value OCP2.

It should be understood that, the second current sensing resistor R2 maybe used to assist the control circuit 143 to determine whether the firstcurrent sensing resistor R1 is shorted. In addition, in the case wherethe first current sensing resistor R1 is shorted, the control circuit143 can determine whether to trigger the protection mechanism accordingto the second current sensing value CS2 so the power apparatus 100 canpass the limited power source test.

In an embodiment of the invention, when the first current sensing valueCS1 is not greater than the first overcurrent protection value OCP1, ifthe first current sensing value CS1 is equal to a reference currentvalue REF and the second current sensing value CS2 is greater than thesecond overcurrent protection value OCP2, the control circuit 143determines that the first current sensing resistor R1 is shorted, andthe control circuit 143 triggers the protection mechanism to limit theoutput current Io of the power conversion circuit 120. Here, thereference current value REF is less than the second overcurrentprotection value OCP2.

In an embodiment of the invention, the reference current value REF is azero current value. However, the invention is not limited to the above,and the reference current value may be determined depending on actualapplications and design requirements.

In an embodiment of the invention, when the control circuit 143 triggersthe protection mechanism, the control circuit 143 can generate a controlsignal for the power conversion circuit 120. The power conversioncircuit 120 can perform an overcurrent protection operation in responseto the control signal to reduce a current value of the output currentIo. The overcurrent protection operation is well-known to persons ofordinary skill in the art and thus not repeated hereinafter.

In an embodiment of the invention, the power apparatus 100 may be, forexample, a PD (Power Delivery) apparatus with adjustable output voltageand output current, but not limited thereto. In an embodiment of theinvention, the power apparatus 100 may be, for example, a PD apparatusin compliance with USB 3.1 power delivery specification.

In an embodiment of the invention, the power conversion circuit 120 maybe, for example, an AC-to-DC converter or a DC-to-DC converter withovercurrent protection functions. Nevertheless, the disclosure is notlimited in this regard. The type of the power conversion circuit 120 isnot particularly limited by the invention.

FIG. 2 is a circuit block diagram illustrating a control circuitaccording to an embodiment of the invention. Referring to FIG. 1 andFIG. 2 together, the control circuit 143 may include an amplifyingcircuit 1433, a first analog-to-digital conversion circuit 1431, asecond analog-to-digital conversion circuit 1432 and a control body1434. The amplifying circuit 1433 is coupled to the two ends of thefirst current sensing resistor R1 to amplify the first sensing voltageVS1 and accordingly generate an amplified voltage VA. The firstanalog-to-digital conversion circuit 1431 is coupled to the amplifyingcircuit 1433 to receive the amplified voltage VA and perform ananalog-to-digital conversion on the amplified voltage VA to generate thefirst current sensing value CS1. The second analog-to-digital conversioncircuit 1432 is directly coupled to the two ends of the second currentsensing resistor R2, and configured to perform the analog-to-digitalconversion on the second sensing voltage VS2 and accordingly generatethe second current sensing value CS2.

The control body 1434 is configured to serve as an operation core of thecontrol circuit 143. Specifically, the control body 1434 is coupled tothe first analog-to-digital conversion circuit 1431 and the secondanalog-to-digital conversion circuit 1432 to receive the first currentsensing value CS1 and the second current sensing value CS2. The controlbody 1434 can compare the first current sensing value CS1 with thereference current value REF and compare the second current sensing valueCS2 with the second overcurrent protection value OCP2. In the case wherethe first current sensing value CS1 is not greater than the firstovercurrent protection value OCP1, if the first current sensing valueCS1 is equal to the reference current value REF and the second currentsensing value CS2 is greater than the second overcurrent protectionvalue OCP2, the control body 1434 determines that the first currentsensing resistor R1 is shorted, and the control body 1434 triggers theprotection mechanism to limit the output current Io of the powerconversion circuit 120. Further, other operation details regarding thecontrol body 1434 may refer to the related description for the controlcircuit 143, which is not repeated hereinafter.

It is worth noting that, in order to reduce a hardware cost of thecontrol circuit 143, there is no amplifying circuit additionallydisposed between the second analog-to-digital conversion circuit 1432and the second current sensing resistor R2. In other words, the secondanalog-to-digital conversion circuit 1432 is directly coupled to the twoends of the second current sensing resistor R2, and directly convertsthe second sensing voltage VS2 into the second current sensing valueCS2. Although such a design may make the accuracy of the second currentsensing value CS2 lower than the accuracy of the first current sensingvalue CS1, with the aid of the determination condition “the firstcurrent sensing value CS1 is equal to the reference current value REFand the second current sensing value CS2 is greater than the secondovercurrent protection value OCP2”, the control circuit 143 can stillcorrectly determine that the output current Io is greater than or equalto the overcurrent value when the first current sensing resistor R1 isshorted, and trigger the protection mechanism so the power apparatus 100can pass the test items of the limited power source.

In an embodiment of the invention, the amplifying circuit 1433 may beimplemented by using an operational amplifier (OPA), but the inventionis not limited thereto. In another embodiment of the invention, theamplifying circuit 1433 may be implemented by adopting the existingvoltage amplifying circuit.

In an embodiment of the invention, the first analog-to-digitalconversion circuit 1431 and the second analog-to-digital conversioncircuit 1432 may be implemented by using the existing analog-to-digitalconverter.

In an embodiment of the invention, the control body 1434 may behardware, firmware, software or machine executable program codes storedin a memory to be loaded and executed by a micro-processor (or amicro-controller). In form of hardware, the control body 1434 may beimplemented by using one single integrated circuit chip, or may beimplemented by using a plurality of circuit chips. However, theinvention is not limited in this regard. The circuit chips or theintegrated circuit chip may be implemented by adopting anapplication-specific integrated circuit (ASIC) or a field programmablegate array (FPGA) or a complex programmable logic device (CPLD). Thememory may be, for example, a random access memory, a read-only memoryor a flash memory.

FIG. 3 is a flowchart illustrating steps in the current detecting methodaccording to an embodiment of the invention, which is applicable to thepower apparatus 100 of FIG. 1 but not limited thereto. Referring to FIG.1 and FIG. 3 together, the current detecting method includes steps S310,S320, S330 and S340. In step S310, the output current Io of the powerapparatus 100 is sensed by the first current sensing resistor R1 toobtain the first sensing voltage VS1. In step S320, the output currentIo is sensed by the second current sensing resistor R2 to obtain thesecond sensing voltage VS2. It should be understood that, step S320 maybe executed prior to step S310, or step S310 and step S320 may beexecuted simultaneously.

Next, in step S330, the first sensing voltage VS1 and the second sensingvoltage VS2 are respectively converted into the first current sensingvalue CS1 and the second current sensing value CS2 by the controlcircuit 143. Then, in step S340, the protection mechanism is triggeredby the control circuit 143 if the first current sensing value CS1 isgreater than the first overcurrent protection value OCP1; and when thefirst current sensing value CS1 is not greater than the firstovercurrent protection value OCP1, the protection mechanism is triggeredby the control circuit 143 if the second current sensing value CS2 isgreater than the second overcurrent protection value OCP2, wherein thefirst overcurrent protection value OCP1 is greater than the secondovercurrent protection value OCP2.

FIG. 4 is a flowchart illustrating detailed steps in step S330 of FIG. 3according to an embodiment of the invention. It should be noted that,steps in FIG. 4 are merely examples and are not intended to limit theorder for executing the detailed steps. Referring to FIG. 1 and FIG. 4together, step S330 includes detailed steps S331 to S333. In step S331,the first sensing voltage VS1 is amplified to generate the amplifiedvoltage VA. Then, in step S332, the analog-to-digital conversion isperformed on the amplified voltage VA to generate the first currentsensing value CS1. On the other hand, in step S333, theanalog-to-digital conversion is directly performed on the second sensingvoltage VS2 to generate the second current sensing value CS2.

FIG. 5 is a flowchart illustrating detailed steps in step S340 of FIG. 3according to an embodiment of the invention. Referring to FIG. 1 andFIG. 5 together, step S340 includes detailed steps S342, S344 and S346.First, in step S342, whether the first current sensing value CS1 isgreater than the overcurrent protection value OCP1 is determined toobtain a first determination result. If the first determination resultis “Yes”, which means that the output current Io is greater than theovercurrent value, the protection mechanism is triggered by the controlcircuit 143 to limit the output current Io, as shown by step S346.Otherwise, if the first determination result is “No”, whether the firstcurrent sensing value CS1 is equal to the reference current value REFand whether the second current sensing value CS2 is greater than thesecond overcurrent protection value OCP2 are determined to obtain asecond determination result, as shown by step S344. If the seconddetermination result is “Yes”, which means that the output current Io isgreater than the overcurrent value, the protection mechanism istriggered by the control circuit 143 to limit the output current Io, asshown by step S346. Otherwise, if the second determination result is“No”, which means that the output current Io is less than theovercurrent value, the process returns to step S310 of FIG. 3 in which anext current detecting operation is performed.

In addition, enough teaching, suggestion, and implementation of thecurrent detecting method in this embodiment of the invention may beobtained from the embodiments of FIG. 1 and FIG. 2, and thus detailsregarding the same are not repeated hereinafter.

In summary, the power apparatus, the current detecting circuit and thecurrent detecting method provided by the embodiments of the inventioncan allow the control circuit to correctly trigger the protectionmechanism by the determination condition “the first current sensingvalue is not greater than the first overcurrent protection value and thesecond current sensing value is greater than the second overcurrentprotection value” in the case where the accuracy of the second currentsensing value is lower than the accuracy of the first current sensingvalue. In this way, not only can the power apparatus could successfullypass the test items of the limited power source, increases of themanufacturing cost of the power apparatus for improving the accuracy ofthe second current sensing value could also be avoided.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentdisclosure without departing from the scope or spirit of the disclosure.In view of the foregoing, it is intended that the present disclosurecover modifications and variations of this disclosure provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A current detecting circuit, comprising: a firstcurrent sensing resistor, configured to sense an output current of apower apparatus to obtain a first sensing voltage; a second currentsensing resistor, configured to sense the output current to obtain asecond sensing voltage; and a control circuit, coupled to two ends ofthe first current sensing resistor and two ends of the second currentsensing resistor to receive the first sensing voltage and the secondsensing voltage, and converting the first sensing voltage and the secondsensing voltage respectively into a first current sensing value and asecond current sensing value, wherein the control circuit triggers aprotection mechanism when the first current sensing value is greaterthan a first overcurrent protection value, wherein when the firstcurrent sensing value is not greater than the first overcurrentprotection value, the control circuit triggers the protection mechanismif the second current sensing value is greater than a second overcurrentprotection value, wherein the first overcurrent protection value isgreater than the second overcurrent protection value, wherein thecontrol circuit comprises: an amplifying circuit, coupled to the twoends of the first current sensing resistor to amplify the first sensingvoltage and accordingly generate an amplified voltage; a firstanalog-to-digital conversion circuit, coupled to the amplifying circuitto receive the amplified voltage and perform an analog-to-digitalconversion on the amplified voltage to generate the first currentsensing value; a second analog-to-digital conversion circuit, directlycoupled to the two ends of the second current sensing resistor, andconfigured to perform the analog-to-digital conversion on the secondsensing voltage and accordingly generate the second current sensingvalue; and a control body, coupled to the first analog-to-digitalconversion circuit and the second analog-to-digital conversion circuitto receive the first current sensing value and the second currentsensing value, wherein when the first current sensing value is notgreater than the first overcurrent protection value, if the firstcurrent sensing value is equal to a reference current value and thesecond current sensing value is greater than the second overcurrentprotection value, the control body determines that the first currentsensing resistor is shorted, and the control body triggers theprotection mechanism to limit the output current, wherein the referencecurrent value is less than the second overcurrent protection value. 2.The current detecting circuit according to claim 1, wherein thereference current value is a zero current value.
 3. A power apparatus,comprising: a power conversion circuit, configured to generate an outputcurrent; and a current detecting circuit, coupled to the powerconversion circuit to detect the output current, the current detectingcircuit comprising: a first current sensing resistor, configured tosense the output current to obtain a first sensing voltage; a secondcurrent sensing resistor, configured to sense the output current toobtain a second sensing voltage; and a control circuit, coupled to twoends of the first current sensing resistor and two ends of the secondcurrent sensing resistor to receive the first sensing voltage and thesecond sensing voltage, and converting the first sensing voltage and thesecond sensing voltage respectively into a first current sensing valueand a second current sensing value, wherein the control circuit triggersa protection mechanism when the first current sensing value is greaterthan a first overcurrent protection value, wherein when the firstcurrent sensing value is not greater than the first overcurrentprotection value, the control circuit triggers the protection mechanismif the second current sensing value is greater than a second overcurrentprotection value, wherein the first overcurrent protection value isgreater than the second overcurrent protection value, wherein thecontrol circuit comprises: an amplifying circuit, coupled to the twoends of the first current sensing resistor to amplify the first sensingvoltage and accordingly generate an amplified voltage; a firstanalog-to-digital conversion circuit, coupled to the amplifying circuitto receive the amplified voltage and perform an analog-to-digitalconversion on the amplified voltage to generate the first currentsensing value; a second analog-to-digital conversion circuit, directlycoupled to the two ends of the second current sensing resistor, andconfigured to perform the analog-to-digital conversion on the secondsensing voltage and accordingly generate the second current sensingvalue; and a control body, coupled to the first analog-to-digitalconversion circuit and the second analog-to-digital conversion circuitto receive the first current sensing value and the second currentsensing value, wherein when the first current sensing value is notgreater than the first overcurrent protection value, if the firstcurrent sensing value is equal to a reference current value and thesecond current sensing value is greater than the second overcurrentprotection value, the control body determines that the first currentsensing resistor is shorted, and the control body triggers theprotection mechanism to limit the output current, wherein the referencecurrent value is less than the second overcurrent protection value. 4.The power apparatus according to claim 3, wherein the reference currentvalue is a zero current value.
 5. A current detecting method,comprising: sensing an output current of a power apparatus by a firstcurrent sensing resistor to obtain a first sensing voltage; sensing theoutput current by a second current sensing resistor to obtain a secondsensing voltage; converting the first sensing voltage and the secondsensing voltage respectively into a first current sensing value and asecond current sensing value by a control circuit; triggering aprotection mechanism by the control circuit if the first current sensingvalue is greater than a first overcurrent protection value; and when thefirst current sensing value is not greater than the first overcurrentprotection value, triggering the protection mechanism by the controlcircuit if the second current sensing value is greater than a secondovercurrent protection value, wherein the first overcurrent protectionvalue is greater than the second overcurrent protection value, whereinthe step of converting the first sensing voltage and the second sensingvoltage respectively into the first current sensing value and the secondcurrent sensing value by the control circuit comprises: amplifying thefirst sensing voltage to generate an amplified voltage; performing ananalog-to-digital conversion on the amplified voltage to generate thefirst current sensing value; and directly performing theanalog-to-digital conversion on the second sensing voltage to generatethe second current sensing value, wherein when the first current sensingvalue is not greater than the first overcurrent protection value, thestep of triggering the protection mechanism by the control circuit ifthe second current sensing value is greater than the second overcurrentprotection value comprises: triggering the protection mechanism by thecontrol circuit to limit the output current if the first current sensingvalue is equal to a reference current value and the second currentsensing value is greater than the second overcurrent protection value,wherein the reference current value is less than the second overcurrentprotection value.
 6. The current detecting method according to claim 5,wherein when the first current sensing value is not greater than thefirst overcurrent protection value, the step of triggering theprotection mechanism by the control circuit if the second currentsensing value is greater than the second overcurrent protection valuecomprises: triggering the protection mechanism by the control circuit tolimit the output current if the first current sensing value is equal toa reference current value and the second current sensing value isgreater than the second overcurrent protection value, wherein thereference current value is less than the second overcurrent protectionvalue.
 7. The current detecting method according to claim 6, wherein thereference current value is a zero current value.